On a perfect Southern California morning not long ago, a gaggle of children gathered in the backyard of a million-dollar home in an upscale Los Angeles neighborhood to celebrate the birthday of twin four-year-old girls. The host parents had rented a petting zoo for the day, and kids jumped gleefully in a bouncy castle out in the driveway. On the terrace, a few parents chatted beside an alluring spread of bagels, coffee and fruit.

Most of the kids at the party attend the same preschool. The father of one child enrolled there, where tuition is $14,300 a year for half a day, was asked what he likes about it.